"Happy 19th Birthday to the little sister I always wanted but never had," Hyland wrote alongside a cute black-and-white shot of herself and Winter. "I know 19 is the most useless age as you get older but think of it as one year closer to your 20s! Love you so much @arielwinter ?."

Winter and Berg, along with a group of friends that included Winter's Modern Family brother, Nolan Gould, recently vacationed together in Bora Bora -- and didn't hold back when it came to posting sexy bikini pics.